Induced Magnetic Anisotropy in Permalloy Deposited with Magnetic Field and Magnetic Annealing

DoctorPermalloy is a soft magnetic material having high permeability. It is known to have wide range of applications such as energy converter and amplifier, magnetic core, magnetic amplifier, shielding, absorber, magnetic memory circuit, sensors, and recently MRAMs as well.Magnetic anisotropy is generated by dipole interaction and spin-orbit interaction and is categorized into Magnetocrystalline Anisotropy, Shape Anisotropy, Magnetoelastic Anisotropy, and Induced Magnetic Anisotropy. Among them, the Induced Magnetic Anisotropy can be controlled with processing technology and affects the magnetic properties by directly relating to coercivity, squareness, initial permeability, and Hysteresis curve shape.It is known that Induced Magnetic Anisotropy is generated by depositing a thin film under magnetic field, by magnetic annealing and quenching, and by depositing after installing a substrate in a slope. This phenomenon explains its origin with strain, atomic pair ordering, and shape irregularity, but it’s difficult to find clear experimental evidence having investigated and observed its origin at the atomic scale. Therefore, this study examines how strain and atomic pair ordering contribute to the induced magnetic anisotropy generation in Permalloy thin films through deposition under magnetic field and annealing with magnetic field. Firstly, 100 nm thick Permalloy thin films were prepared by deposition under magnetic field. Then strain was measured carefully, i.e. interplanar distance between crystallographic (111) planes in various directions, using high power synchrotron radiation and precise Grazing Incidence X-Ray Diffraction (GIXRD) method. It was identified that Field Induced Magnetic Anisotropy was formed in the thin films through deposition under magnetic field. The d(111) values that increase in proportion to the intensity of magnetic field and changes in coercive force after annealing of thin films deposited under magnetic field were examined and based on the results, it was identified that Field Induced Strain and Field Induced Magnetic Anisotropy were closely linked. Through a value 1.359×10-4 obtained by calculating the strain, it was identified that the Induced Magnetic Anisotropy caused by deposition under magnetic field resulted from Field Induced Strain instead of Directional Pair Ordering.Secondly, the effect of magnetic field annealing on Permalloy thin films was investigated through characterization of the crystal structure and magnetic properties. Highly a-axis oriented Fe21Ni79 films were formed on Si substrates by magnetic field annealing. Uniform distribution of grains and columnar grain growth were dominant for the films annealed with magnetic field. It was identified that Induced Magnetic Anisotropy was formed through annealing under magnetic field. Through EXAFS analysis, 1.19×10-3 was obtained as the strain of a specimen annealed under magnetic fieldand through this value, it was identified that Induced Magnetic Anisotropy was formed by Directional Pair Ordering rather than by Field Induced Strain